MICROWAVE ASSISTED MAGNETIC RECORDING SYSTEM
A microwave assisted magnetic recording system includes a write pole that generates a write magnetic field, an element that generates a radio frequency assist magnetic field, and a recording medium that moves relative to the write pole. The recording medium is exposed to the radio frequency assist magnetic field before it is exposed to the write magnetic field. One possible element that generates the radio frequency assist magnetic field is an assist wire placed perpendicular to the write pole. Alternatively, the assist wire can be placed parallel to the write pole so that its radio frequency assist magnetic field couples with the write pole, which in turn generates its own coupled radio frequency magnetic field along with the write magnetic field.
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This application claims benefit from U.S. provisional patent application No. 61/046,676, entitled “OPTIMIZATION OF MICROWAVE ASSISTED MAGNETIZATION REVERSAL,” filed Apr. 21, 2008 by K. Rivkin et al., which is incorporated by reference.
BACKGROUNDThis invention relates generally to the field of electronic data storage and retrieval systems. In particular, the present invention relates to a microwave assisted recording system.
A magnetic data storage and retrieval system typically includes a writer for storing magnetically encoded information on a magnetic medium and a reader for retrieving the magnetically encoded information from the magnetic medium. The writer typically includes one or more magnetic poles surrounded by a conductive coil. To write data to the magnetic medium, a time varying write current is caused to flow through the conductive coil, which in turn produces a time varying magnetic field through the poles. The magnetic medium is then passed near the air bearing surface (ABS) of the writer at a predetermined distance such that the medium passes through the magnetic field. As the write current changes in direction and magnitude, the magnetic field changes in direction and magnitude as well. In a typical magnetic writer, a sufficient magnetic field must be applied to write to the magnetic medium. More specifically, the field produced by the head at the magnetic medium must be of sufficient magnitude to overcome the high coercivity of the magnetic medium.
As data storage densities in magnetic recording continue to progress in an effort to increase the storage capacity of hard disc drives, magnetic transition (bit) dimensions and recording head critical features are being pushed below 100 nm. In addition, making the recording medium stable at higher areal densities requires magnetically harder (high coercivity) storage medium materials. Typically, writing on such media requires a high magnitude magnetic field. Currently, magnetic writers are based on the idea of focusing the magnetic field from the pole towards the magnetic media.
It has been proposed that the effective writability to magnetic media can be improved if addition to a “direct current” (DC) write field (i.e. a magnetic field with a frequency below 5 GHz) created by the writer and possibly other sources, a radio frequency (RF) assist field is simultaneously applied to the media. This type of recording is referred to as microwave assisted magnetic recording (MAMR). In a conventional setup the RF assist fields are required to coincide in the media spatially with the DC or low frequency write fields. Several factors, however, limit the practicality of this writing method, including the fact that the effective writability gradient depends on both RF and DC gradients and their mutual alignment and the need to create sufficiently high RF assist fields.
SUMMARYThe present invention is a microwave assisted magnetic recording system that includes a write pole that generates a write magnetic field and an element that generates a radio frequency assist magnetic field. A recording medium moves relative to the write pole and is subjected to the radio frequency magnetic field prior to being subjected to the direct current magnetic field.
Another aspect of the invention is a microwave assisted magnetic recording system that includes a write pole that generates a write magnetic field and an element that generates a radio frequency assist magnetic field that couples to the write field in a plane parallel to the recording medium such that precession of magnetization in the write pole creates a coupled radio frequency magnetic field.
Another aspect of the invention is a microwave assisted magnetic recording system that includes a write pole that generates a write magnetic field and an element that generates a radio frequency assist magnetic field that is substantially circularly polarized. A recording medium moves relative to the write pole and is subjected to the substantially circularly polarized radio frequency magnetic field prior to being subjected to the direct current magnetic field.
In another aspect, the invention uses a recording medium comprised of multiple recording layers of varying anisotropies which couple the recording medium to the radio frequency assist magnetic field.
RF field source 14 generates RF assist field MRF at or near leading edge 22 of write pole tip 18. RF field source 14 can include an RF generator as well as any element capable of emitting a radio frequency magnetic field such as an antenna, wire, or other like apparatuses. Thus, as magnetic medium 20 moves in the x-direction with respect to write pole tip 18, it is subjected to RF field MRF prior to being subjected to DC field MW. More specifically, RF field MRF is responsible for creating a resonant frequency in magnetic medium 20 that lowers the effective coercivity of magnetic medium 20 before magnetic medium 20 is subjected to the maximum amplitude of DC field MW. This configuration is referred to as a “preassist” configuration, i.e. when RF field MRF precedes DC field MW in magnetic medium 20. Domains 30, 32, 34, and 36 are passed through RF field MRF and magnetization directions in domains 38 and 40 are reversed (in the y-axis direction) when they are subjected to DC field MW.
Magnetic medium 20 is disposed under write pole tip 18 and moves in the x-direction shown in
RF field MRF is generally elliptically polarized; the direction of RF field MRF follows an elliptical path as a function of time in the ABS 24 (x-z) plane. In a preassist configuration such as MAMR system 10 in
Magnetic medium 20 can be a multilayer recording medium as depicted in
RF field source 14 generates RF assist field MRF. RF field source 14 in this particular embodiment is assist wire 26, of which only a section or portion is shown. Assist wire 26 is placed at leading edge 22 of write pole 16 running perpendicular to write pole 16 (parallel to z-axis). Current IRF is passed through assist wire 26 to create RF field MRF. Current IRF is typically an alternating current at a radio frequency and per the right hand rule creates RF field MRF in magnetic medium 20 in ABS (x-z) plane. Because assist wire 26 is placed on leading edge 22, RF field MRF is generated upstream of DC field MW and magnetic medium 20 is subjected to RF field MRF prior to being subjected to DC field MW. Or, more specifically, RF field MRF is responsible for creating a resonant frequency in magnetic medium 20 that lowers the effective coercivity of magnetic medium 20 before magnetic medium 20 is subjected to the maximum amplitude of DC field MW. This configuration is referred to as a “preassist” configuration, i.e. when RF field MRF precedes DC field MW in magnetic medium 20. Recording layer 42 which contains domains 30, 32, 34, and 36 is passed through RF field MRF and magnetization directions in domains 38 and 40 are reversed when they are subjected to DC field MW. The same activity occurs in domain groups 50 and 52 in recording layers 44 and 46.
Magnetic medium 20 is disposed under write pole tip 18 and moves in the x-direction shown in
An RF assist field in this particular embodiment is produced by RF assist field source 14 and a combination of assist wire 26 (of which only a section or portion is shown) and write pole 16 itself, which is excited by the RF field created by assist wire 26. Assist wire 26 is placed at leading edge 22 of write pole 16 parallel to write pole 16 (parallel to y-axis). Current IRF is passed through assist wire 26 to create an RF field. In this particular embodiment shown in
Magnetic medium 20 is disposed under write pole 16 and moves in the x-direction shown in
As previously discussed, RF assist field MRF is generally elliptically polarized. Also previously discussed were the differences between linearly polarized and circularly polarized RF fields. In the embodiment shown in
RF field source 14 in this particular embodiment is a combination of assist wire 26, of which only a section or portion is shown, and write pole 16 itself, which is excited by the RF field created by assist wire 26. Assist wire 26 is placed at trailing edge 23 of write pole 16 parallel to write pole 16 (parallel to y-axis). Current IRF is passed through assist wire 26 to create an RF field. In this particular embodiment shown in
Magnetic medium 20 is disposed under write pole 16 and moves in the x-direction shown in
As discussed in regards to
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention. The implementations described above and other implementations are within the scope of the following claims.
Claims
1. A microwave assisted magnetic recording system comprising:
- a write pole that generates a write magnetic field;
- a write assist element that generates a radio frequency assist magnetic field; and
- a recording medium that moves relative to the write pole, where the recording medium is subjected to the radio frequency assist magnetic field prior to being subjected to the write magnetic field.
2. The microwave assisted magnetic recording system of claim 1 wherein the radio frequency assist magnetic field is elliptically polarized.
3. The microwave assisted magnetic recording system of claim 1 wherein the radio frequency assist magnetic field is substantially circularly polarized.
4. The microwave assisted magnetic recording system of claim 1 wherein the radio frequency assist magnetic field is substantially linearly polarized.
5. The microwave assisted magnetic recording system of claim 1 wherein the write assist element is an assist wire positioned perpendicular to the write pole adjacent a leading edge of the write pole.
6. The microwave assisted magnetic recording system of claim 1 wherein the write assist element that generates a radio frequency assist magnetic field couples to the write pole in a plane parallel to the recording medium such that precession of magnetization in the write pole creates a coupled radio frequency assist magnetic field.
7. The microwave assisted magnetic recording system of claim 1 wherein the recording medium is comprised of a plurality of recording layers of varying anisotropies which couple the recording medium to the radio frequency assist magnetic field.
8. A microwave assisted magnetic recording system comprising:
- a write pole that generates a write magnetic field;
- a recording medium that moves relative to the write pole; and
- a write assist element that generates a radio frequency assist magnetic field that couples to the write pole in a plane parallel to the recording medium such that precession of magnetization in the write pole creates a coupled radio frequency assist magnetic field.
9. The microwave assisted magnetic recording system of claim 8 wherein the recording medium is subjected to the coupled radio frequency assist magnetic field before it is subjected to the write magnetic field.
10. The microwave assisted magnetic recording system of claim 9 wherein the write assist element is an assist wire positioned on a leading edge of the write pole and parallel to the write pole.
11. The microwave assisted magnetic recording system of claim 10 wherein the coupled magnetic field is elliptically polarized.
12. The microwave assisted magnetic recording system of claim 10 wherein the coupled magnetic field is substantially circularly polarized.
13. The microwave assisted magnetic recording system of claim 10 wherein the couple magnetic field is substantially linearly polarized.
14. The microwave assisted magnetic recording system of claim 8 wherein the write assist element is an assist wire positioned adjacent a trailing edge of the write pole and parallel to the write pole.
15. The microwave assisted magnetic recording system of claim 8 wherein the recording medium is comprised of a plurality of recording layers of varying anisotropies which couple the recording medium to the coupled radio frequency magnetic field.
16. A microwave assisted magnetic recording system comprising:
- a write pole that generates a write magnetic field;
- a write assist element that generates a radio frequency assist magnetic field that is substantially circularly polarized; and
- a recording medium that moves relative to the write pole, where the recording medium is subjected to the substantially circularly polarized radio frequency assist magnetic field prior to being subjected to the write magnetic field.
17. The microwave assisted magnetic recording system of claim 16 wherein the recording medium is subjected to the substantially circularly polarized radio frequency assist magnetic field at the same time as it is subjected to the write magnetic field.
18. The microwave assisted magnetic recording system of claim 16 wherein the recording medium is comprised of a plurality of recording layers of varying anisotropies which couple the recording medium to the circularly polarized radio frequency assist magnetic field.
Type: Application
Filed: Apr 21, 2009
Publication Date: Oct 22, 2009
Patent Grant number: 9449618
Applicant: Seagate Technology LLC (Scotts Valley, CA)
Inventors: Kirill Aleksandrovich Rivkin (Edina, MN), Ned Tabat (Chanhassen, MN)
Application Number: 12/427,534
International Classification: G11B 5/127 (20060101);